21609985920 has 512 divisors, whose sum is σ = 76001587200. Its totient is φ = 5202247680.

The previous prime is 21609985909. The next prime is 21609985921. The reversal of 21609985920 is 2958990612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21609985921) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 109695262 + ... + 109695458.

It is an arithmetic number, because the mean of its divisors is an integer number (148440600).

Almost surely, 2^21609985920 is an apocalyptic number.

21609985920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21609985920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38000793600).

21609985920 is an abundant number, since it is smaller than the sum of its proper divisors (54391601280).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21609985920 is a wasteful number, since it uses less digits than its factorization.

21609985920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 366 (or 354 counting only the distinct ones).

The product of its (nonzero) digits is 699840, while the sum is 51.

The spelling of 21609985920 in words is "twenty-one billion, six hundred nine million, nine hundred eighty-five thousand, nine hundred twenty".